+ let demod table varlist subterm pos context =
+ let cands = IDX.DT.retrieve_generalizations table subterm in
+ list_first
+ (fun (dir, (id,lit,vl,_)) ->
+ match lit with
+ | Terms.Predicate _ -> assert false
+ | Terms.Equation (l,r,_,o) ->
+ let side, newside = if dir=Terms.Left2Right then l,r else r,l in
+ try
+ let subst, varlist =
+ Unif.unification (varlist@vl) varlist subterm side
+ in
+ if o = Terms.Incomparable then
+ let side = Subst.apply_subst subst side in
+ let newside = Subst.apply_subst subst newside in
+ let o = Order.compare_terms newside side in
+ (* Riazanov, pp. 45 (ii) *)
+ if o = Terms.Lt then
+ Some (context newside, subst, varlist, id, pos, dir)
+ else
+ ((*prerr_endline ("Filtering: " ^
+ Pp.pp_foterm side ^ " =(< || =)" ^
+ Pp.pp_foterm newside ^ " coming from " ^
+ Pp.pp_unit_clause uc );*)None)
+ else
+ Some (context newside, subst, varlist, id, pos, dir)
+ with FoUnif.UnificationFailure _ -> None)
+ (IDX.ClauseSet.elements cands)
+ ;;
+
+ (* XXX: possible optimization, if the literal has a "side" already
+ * in normal form we should not traverse it again *)
+ let demodulate_once bag (id, literal, vl, pr) table =
+ debug ("Demodulating : " ^ (Pp.pp_unit_clause (id, literal, vl, pr)));
+ let t =
+ match literal with
+ | Terms.Predicate t -> t
+ | Terms.Equation (l,r,ty,_) -> Terms.Node [ Terms.Leaf B.eqP; ty; l; r ]
+ in
+ match first_position [] (fun x -> x) t (demod table vl) with
+ | None -> None
+ | Some (newt, subst, varlist, id2, pos, dir) ->
+ build_clause bag (fun _ -> true) Terms.Demodulation
+ newt subst varlist id id2 pos dir
+ ;;
+
+ let rec demodulate bag clause table =
+ match demodulate_once bag clause table with
+ | None -> bag, clause
+ | Some (bag, clause) -> demodulate bag clause table
+ ;;
+
+ (* move away *)
+ let is_identity_clause = function
+ | _, Terms.Equation (_,_,_,Terms.Eq), _, _ -> true
+ | _, Terms.Predicate _, _, _ -> assert false
+ | _ -> false
+ ;;
+
+ let is_subsumed ~unify (id, lit, vl, _) table =
+ match lit with
+ | Terms.Predicate _ -> assert false
+ | Terms.Equation (l,r,ty,_) ->
+ let retrieve = if unify then IDX.DT.retrieve_unifiables
+ else IDX.DT.retrieve_generalizations in
+ let lcands = retrieve table l in
+ let rcands = retrieve table r in
+ let f b c =
+ let dir, l, r, vl =
+ match c with
+ | (d, (_,Terms.Equation (l,r,ty,_),vl,_))-> d, l, r, vl
+ |_ -> assert false
+ in
+ let l, r = if (dir = Terms.Left2Right) = b then l,r else r,l in
+ Terms.Node [ Terms.Leaf B.eqP; ty; l; r ], vl
+ in
+ let cands1 = List.map (f true) (IDX.ClauseSet.elements lcands) in
+ let cands2 = List.map (f false) (IDX.ClauseSet.elements rcands) in
+ let t = Terms.Node [ Terms.Leaf B.eqP; ty; l; r ] in
+ let locked_vars = if unify then [] else vl in
+ List.exists
+ (fun (c, vl1) ->
+ try ignore(Unif.unification (vl@vl1) locked_vars c t); true
+ with FoUnif.UnificationFailure _ -> false)
+ (cands1 @ cands2)
+ ;;
+
+ (* demodulate and check for subsumption *)
+ let forward_simplify table bag clause =
+ let bag, clause = demodulate bag clause table in
+ if is_identity_clause clause then None
+ else
+ if is_subsumed ~unify:false clause table then None
+ else Some (bag, clause)
+ ;;